Neurotrophic factors are naturally-occurring proteins that regulate neuronal survival during development and regulate plasticity and structural integrity of the adult nervous system. These neurotrophic factors can be classified into superfamilies, families, subfamilies and individual species based on their structure and function.
Neurotrophic factor superfamilies include the fibroblast growth factor (FGF) superfamily, the neurotrophin superfamily, and the transforming growth factor-β (TGF-β) superfamily. The glial cell line-derived neurotrophic factor (GDNF)-related ligands are a family of proteins within the TGF-β superfamily. GDNF-related ligands include GDNF, persephin (PSP), neurturin (NTN) and neublastin (NBN; known as artemin or enovin). Members of the GDNF-related ligand family are distinguished by, among other things, their seven conserved cysteine residues. These residues form intramolecular and intermolecular disulfide bridges and give rise to the tertiary and quaternary structure of the dimerized polypeptide ligand. Members of the family also induce signaling through a multicomponent receptor complex consisting of a glycosylphosphatidylinositol (GPI)-anchored co-receptor of the GFRα family, a member of the GDNF-related ligand subfamily, and the RET tyrosine kinase receptor.
Activated RET initiates a signal transduction cascade that is responsible, at least in part, for the downstream effects of GDNF-related ligands.
Neublastin is classified within the GDNF family because it shares regions of homology with other GDNF ligands including the seven cysteine motif (e.g., as described in EP02/02691, PCT publications US02/02319 and US02/06388), and because binds to, and activates, the RET receptor as part of a GFRα complex. Neublastin is highly selective for binding to the GFRα3-RET receptor complex. In that respect, neublastin contains unique sub regions in its amino acid sequence as compared with other members of the GDNF-related ligand family.
Administration of neublastin is potentially useful in the treatment of diseases associated with neuronal degeneration and dysfunction. However, neublastin is rapidly cleared by the body, which may affect the neublastin dosing paradigm required in therapeutic applications. There is a need for molecules that display the biological activity of neublastin while exhibiting enhanced potency.